This invention relates to an amplifier arrangement comprising a first amplifier having a first output terminal for connection to a first terminal of a load, and having at least a first transistor for supplying a first current related to a first load current flowing via the first output terminal, first means for generating a first signal which is a measure of the first current, a second amplifier having a second output terminal for connection to a second terminal of the load, and having at least a second transistor for supplying a second current related to a second load current flowing via the second output terminal, second means for generating a second signal which is a measure of the second current, and protection means for limiting the first and the second load current in order to protect the first and the second amplifier.
In general, such an amplifier arrangement can be used for driving a load coupled between two amplifiers, which amplifiers are protected against supplying excessive load currents, and in particular the arrangement is suitable for use in car radios, where short circuits to ground always constitute a problem.
Such an amplifier arrangement is generally known because most amplifier arrangements comprise a protection device for protecting the amplifiers used in the arrangement. This protection device comprises means for generating one or more signals which are each a measure of a current or voltage related to the load currents and also comprises protection means which are responsive to said signals to limit the load currents. In amplifier arrangements of the type defined in the opening paragraph the two amplifiers are each protected in a substantially identical way. One possibility of implementing the protection of an amplifier is disclosed in European Patent Application 0,132,863. In said amplifier the signal generating means generate two signals, which are measures of a load-current-related current and voltage, respectively, and the protection means comprise a control amplifier. This control amplifier is driven if the difference between the two signals exceeds a threshold value and thereby limits the amplifier drive and thus the load current. The known protection devices protect the amplifiers against short-circuits to ground, but comparatively small short-circuit currents are not detected. These short-circuit currents give rise to a loss of power and may cause thermal damage to the amplifier arrangement.